diff --git a/setup.py b/setup.py
index 8f5c347c..a0512a0e 100755
--- a/setup.py
+++ b/setup.py
@@ -144,6 +144,9 @@ setup(
         'gadjo',
         'phpserialize',
         'suds',
+        # pyexcel-xlsx is unmaintained (no change since 2020) and is incompatible
+        # with a change introduced in openpyxl 3.1.0
+        'openpyxl<3.1',
         'pyexcel-io',
         'pyexcel-ods',
         'pyexcel-xls',